Physalia (Bluebottle, Portuguese man-of-war)

Bluebottles float around in the ocean and are notorious for their long tentacles (up to 10 m long) that sting people swimming in the water. Each bluebottle consists of a colony of individuals that function together as a single integrated animal.

Porpita (Raft hydroid)

Has a round, flat gas-filled float. Harmless to people.

Velella (By-the-wind sailor)

 The float carries a vertical piece of tissue that functions as a sail.